If a formula implements startup_plist it has out-of-the-box support by
brew services. If not it's possible to specify the path to a plist file:
`brew services couchdb-lucence /usr/local/Cellar/..../couchdb-lucene.plist`.
FixesHomebrew/homebrew#3422.
Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
